Recently, an apparatus complying with a system such as MPEG (Moving Picture Experts Group), which digitally treats image information and compresses the same by an orthogonal transform such as a discrete cosine transform and motion compensation by using redundancy specific to the image information in order to efficiently transmit and accumulate the information at that time, has been widely used in both of information distribution in a broadcast station and information reception in standard home.
These days, there are growing needs for higher compression coding such as coding of an image of approximately 4096×2048 pixels, four times as many as those for a high-definition image, or distribution of the high-definition image in an environment of limited transmission capacity such as the Internet. Therefore, VCEG under ITU-T continuously studies improvement in coding efficiency.
A pixel size of a macroblock being a partial area of the image, which is a division unit (unit of coding process) of the image at the time of image coding in MPEG1, MPEG2, and ITU-T H.264/MPEG4-AVC being conventional image coding systems, is always 16×16 pixels. On the other hand, Non-Patent Document 1 suggests extending the number of pixels of the macroblock horizontally and vertically as elemental technology of next-generation image coding standard. This also suggests using the macroblock of 32×32 pixels and 64×64 pixels in addition to the pixel size of the macroblock of 16×16 pixels defined by the MPEG1, MPEG2, ITU-T H.264/MPEG4-AVC and the like. This is for improving the coding efficiency by performing the motion compensation and the orthogonal transform in a unit of larger area in areas with similar motion because it is predicted that the pixel size of the image to be coded increases horizontally and vertically in the future such as UHD (Ultra High Definition; 4000 pixels×2000 pixels), for example.
Non-Patent Document 1 adopts a hierarchical structure, thereby defining a larger block as a superset for the block not larger than 16×16 pixels while maintaining compatibility with the macroblock of current AVC.
Although Non-Patent Document 1 suggests applying the extended macroblock to inter slice, Non-Patent Document 2 suggests applying the extended macroblock to intra slice.